This invention relates, in general, to hybrids, and more specifically, to microwave ring hybrids.
Ring hybrids have been widely used in radio and microwave communications for two or three decades. Ring hybrids are also used in mobile and cellular radios, and satellite communication systems.
Ring hybrids, or directional couplers, were originally constructed using transmission lines. The transmission lines of the ring hybrids extend in a circle and have a number of terminal branches projecting from the circular wave path at given intervals. The electrical lengths of the transmission lines are determined and arranged such that power will be present at certain of the terminals with given phase differentials. Power at the other terminals will be zero since the phase differential between signals at the zero terminals will cancel. Ring hybrids incorporating transmission lines supply broad frequency bandwidths. A ring hybrid demonstrating these characteristics is described in U.S. Pat. No. 3,229,233, Variable Power Division Hybrid Ring Directional Coupler issued Jan. 11, 1966 to Chuck Y. Pon and assigned to Textron Inc.
With the advent of MMIC (monolithic microwave integrated circuit) technology, space restrictions were imposed on circuitry. Transmission lines were incompatible with MMIC circuits and chips. A basic need is to incorporate as much of the circuitry on a single small chip as possible. As size decreases, particularly with hybrids such as ring hybrid, the bandwidth diminishes.